Question

A person bending forward to lift a load "with his back" rather than"with his knees" can be injured by large forces exerted on themuscles and vertebrae

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asked 2021-03-24
A person bending forward to lift a load "with his back" rather than"with his knees" can be injured by large forces exerted on themuscles and vertebrae. A person is bending over to lift a200-N object. The spine and upper body are represented as auniform horizontal rod of weight 350 N, pivoted at the base of thespine. The erector spinalis muscle, attached at a pointtwo-thirds of the way up the spine, maintains the position of theback. The angle between the spine and this muscle is 12degrees. Find the tension in the back muscle and thecompressional force in the spine.

Answers (1)

2021-03-26
image
You have not given the free body diagram which is very necessary to understand
Anyway, I amgiving the diagram. We assume the length of the spine is L
Taking the torques about A
\(\displaystyle?={350}\cdot{\frac{{{L}}}{{{2}}}}+{200}\cdot{L}-{T}{\sin{{12}}}\cdot{\left({\frac{{{2}}}{{{3}}}}\right)}{L}={0}\)
solve for T
b) Taking the forces about the x direction.
\(\displaystyle{F}_{{x}}={R}_{{x}}-{T}{\cos{{12}}}={0}\)
Substitutingfor T solve for \(\displaystyle{R}_{{x}}\)
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